Series of Highway Shootings Unnerves Phoenix

A series of shootings over nearly two weeks along highways in the Phoenix area, most involving the same stretch of Interstate 10, has alarmed residents and confounded the police.

The authorities reported another shooting early Thursday involving a tractor-trailer pierced through the side by a bullet, bringing the total number of incidents to 11 since Aug. 29. Eight of those involved bullets, and three involved “projectiles,” officials said.

Only one minor injury has been reported: A 13-year-old girl was cut when a bullet shattered a window of the car she was in.

For many Phoenix-area residents, the incidents have revived troubling memories of the last time their city was terrorized by a string of shootings. In 2006, Dale S. Hausner and Samuel J. Dieteman were arrested and charged with murder after a yearlong series of attacks.

Mr. Hausner, who was sentenced to six death penalties, died in his cell in 2013 after overdosing on antidepressants. Mr. Dieteman is serving a life sentence.

Bart Graves, a spokesman for the Arizona Department of Public Safety, played down the connection, saying the latest shootings are “not even close to being reminiscent of those.”

“That was people randomly being shot and killed on the streets,” he said.

He added that while people in Phoenix were very aware of the shootings, some had asked the department not to publicize them too much because “they didn’t want to create copycats.”

“If he or she is doing it in the middle of the day, it’s a scary situation,” Tim Case, a Department of Public Safety spokesman, told reporters. He said the case was the department’s No. 1 priority.

Gov. Douglas Ducey asked for the public’s help in a Twitter post on Thursday.

Tips have been pouring into the hotline. “They want this solved as we do,” Mr. Graves said.

The Arizona Department of Public Safety, which has partnered in its investigation with the Federal Bureau of Investigation, the Bureau of Alcohol, Tobacco, Firearms and Explosives and the police departments of Phoenix and Tempe, is offering a $20,000 reward for information leading to the arrest and conviction of the gunman or gunmen.

“It is just a matter of time if this behavior continues that we have tragedy on our roadways,” said the department’s head, Col. Frank Milstead.